In an separate directive, the agency also ordered the sanitary district to pack the spaces between the barriers with clay.
The order also cited an anonymous allegation that some of the overflowing sewage had reached the Merrimack River a few hundred yards to the west, which plant operators have denied. Worrall said the allegation was relayed to the DEC by a North Andover conservation official, who told the DEP she received “complaints of a sludge/sewage discharge to the Merrimack River via a wetlands/stream area emanating from the facility.”
Jennifer Hughes, North Andover’s conservation administrator, could not be reached yesterday.
Susan Sawyer, the director of the town’s Health Department, said the department has not had an active role in the cleanup because the treatment plant is in an isolated and buffered corner of the town and the spills are not a threat to residents. The plant is off Charles Street, between the runways of the Lawrence Municipal Airport on the north, east and south and the Merrimack River on the west.
“The people it’s affecting most are the people working with it,” Sawyer said. “The citizens aren’t at any risk. We’re counting on the DEP.”
The waste inside each of the 1.4 million-gallon tanks is in an early stage of treatment and still contains coliform bacteria and other pathogens that can cause a range of diseases, including hepatitis A, typhoid and salmonellosis.
Richard Hogan, the executive director of the sanitary district, said earlier this month that the cause of the viscous, black waterfalls pouring from the tops of the tanks is uncertain and said there is no known fix except to allow it to run its course. He said other overflows have occurred before, most recently about two years ago.
The overflows are not unusual in treatment tanks with similar designs nationwide, which have unsealed caps that float on top of the gases inside.